In depth percentage calculation, which measurement is used as the denominator?

• A. Table width
• B. Girdle diameter
• C. Crown height
• D. Culet size

Answer: (B)

Depth percentage expresses how deep the diamond is relative to its width. The measurement used in the denominator is the diameter of the stone, typically the girdle diameter measured across the widest point. The depth is the vertical distance from the table to the culet along the center axis, and depth percentage is calculated as overall depth divided by the average girdle diameter, times 100. If the stone isn’t perfectly round, you use the average of two perpendicular girdle diameters to get that width. The other measurements—table width, crown height, and culet size—are used for other proportion considerations and do not serve as the denominator in depth percentage.